The common practice in industry, particularly the petroleum industry, to measure the effect of de-emulsifiers on the stability of emulsions is the so called “Bottle test”. A glass bottle filled with measured amounts of oil (such as crude oil, bitumen, heavy oil, etc.), water and de-emulsifiers will be provided. After creating the emulsion by shaking the bottle, the emulsion will be left for a certain period of time so that the separation of the water from the oil can occur. The amount of water liberated from the emulsion is a measure of efficiency of the de-emulsifier. This test has to be repeated many times due to the different available de-emulsifiers and their wide spectrum of concentration. Furthermore, the type of crude oil varies from one reservoir to another, so finding the best match for every specific oil is a very time consuming task. “Bottle test” is inherently a low-tech which does not provide any insight about the film properties and its lack of automation reveals the need for a better measurement platform.
The presence of water droplets in crude oil can result in a very stable emulsion system. Stabilizer molecules in oil adsorb on the surface of the water droplets and make a resistant shield that prevents them from coalescence. Most of the water in such water-oil emulsions can be removed using density difference methods such as gravitational or centrifugal separations. However, the remaining 1 or 2% of the water that exists in the form of micro droplets (less than 5 μm) is difficult to separate using conventional techniques. The density difference methods do not separate such droplets due to insignificant gravitational or centrifugal forces. De-emulsifiers are used to increase the chance of coalescence of micron size droplets by means of reducing interfacial tension of the water/oil system. De-emulsifiers are generally complex polyelectrolytes or mixtures of polyelectrolytes, which specifically interact with the oil-water interfaces to destabilize emulsions. Therefore, the procedure of identifying the best de-emulsifiers for a specific type of oil using the “bottle test” may take days, which makes it quite difficult to change the amount or type of the de-emulsifier during production. Time is also very crucial in oil spill remediation issues, which underscores the need for better and faster de-emulsifier identification methods. Alternatively, the stability of these emulsion systems and the effect of de-emulsifiers can be studied experimentally on a thin film of oil formed between two water droplets. Experimental techniques such as the Thin Liquid Film (TLF) apparatus or the Sheludko cell, and the Micropipette experiment may be used to create thin liquid films and measure their characteristics. The thin liquid film of oil is ruptured using an external force such as pressure or electric field. The pressure or the electric field at which the film breaks is the measure of stability of the interface.
The thin liquid film apparatus (TLF) is a well-known and widely used method to create and study the stability of thin liquid films. It employs a porous glass plate in which a millimeter size circular hole is drilled. The plate is connected to a capillary, which is filled with oil. The plate is then immersed in an electrolyte solution. Simultaneous adjustment of the pressure of the electrolyte solution and the oil in the capillary results in formation of an oil film inside the hole. The film developed can be considered as an analogue of two large (millimeter scale) water droplets separated by a thin oil film. By increasing the electrolyte's pressure, the two water phases can be pushed toward each other, thereby altering the film thickness. Using interferometry techniques, the thickness of the film can be measured accurately. The micropipette method can also be used to study thin liquid films. It consists of two micropipettes, at the tips of which water droplets are formed. The two pipettes are immersed in the oil phase while pressing the two water droplets onto each other. The oil film created between the droplets can be broken by moving the micropipettes closer. This can result in characterization of the film stability. This method is not capable of measuring the thickness of the film directly.